In the photographic reproduction sector, light-sensitive reproduction materials are used in which differences in the tackiness of the exposed and unexposed areas of the light-sensitive layer are utilized to produce the image. Thus a reproduction process is known, e.g., from German Pat. Nos. 1,210,321 (U.S. Pat. No. 3,060,024), 1,904,058 (U.S. Pat. No. 3,620,726), 1,904,059 (U.S. Pat. No. 3,582,327), and 2,004,214, in which a tacky photopolymerizable reproduction material comprising a layer support and a photopolymerizable layer that contains at least one addition polymerizable monomer and a photo-polymerization initiator is hardened by imagewise exposure, whereby the exposed image areas lose their tackiness. The latent image is then made visible by applying suitable toner materials that only adhere to the unexposed tacky areas, whereas they can be removed from the exposed non-tacky image areas after application. Using this method, positive optionally colored images of the original are obtained that in appearance resemble images produced using printing inks. The process has therefore gained considerable practical importance for the proofing of color separations, especially in the printing industry.
The toner materials, consisting predominantly of finely divided powders, can be applied by dusting the imagewise exposed surface with the toner. According to another embodiment, the toner can be a layer of finely divided particles loosely bound on a separate support, which is transferred by bringing this support into contact with the imagewise exposed layer and applying heat. Thus it is known, e.g., from DE-PS No. 1,205,117 (U.S. Pat. No. 3,060,025), to use for this purpose a transfer layer comprising a thermoplastic binder and the toner material, applied onto a layer support.
Pigmented layers for the production of colored images are known from DE-PS No. 2,949,462 (U.S. Pat. No. 4,275,140) that contain 75-95 parts by weight of pigment and 25-5 parts by weight of an elastomeric binder. According to this process images of high opacity are obtained that are preferably used for the reproduction of brochures and exhibits. Due to their high opacity, however, such pigmented layers are not suitable for color proofing. Reducing the pigment content drastically does lead to a reduced density, but causes total loss of resolution. This state of affairs is illustrated in more detail in the examples.
It has not been possible hitherto to use these transfer layers to produce reproductions that meet the exacting requirements of the color-proofing industry for high-quality prints, above all with respect to the achievable resolution and uniformity of the tonal values over larger surfaces. In practice, therefore, the tacky areas can only be satisfactorily toned by dusting the exposed layer with finely divided powders, either by hand or using automatic applicators, although the use of a transfer layer would be much simpler, cleaner, and less polluting.
It is known in reproduction technology to use screened color separations as copy originals for the production of offset- or relief printing plates. Before the printing plates are exposed, the color separations are checked using color proofing methods to ascertain whether the later printing result will represent a reproduction of the original that has correct tonal values. According to general industry standards, a resolution of 2%-98% dots with a screen width of 60 lines/cm is required for a high-quality offset print. It is particularly difficult to achieve satisfactory resolution of the sharp 2% dots in the highlights and the 98% dots in the shadows. It is also of considerable importance for a good tonal value reproduction that dots of the same size have sharp edges over the entire surface area and be reproduced uniformly, i.e. without variations in their size.
It is therefore the object of the present invention to give a process for the production of reproductions on tonable light-sensitive layers which utilizes a transfer layer containing at least one finely divided powder and/or a dissolved dye, with which the resolution required by the printing industry can be achieved and that moreover excels in the high uniformity of its tonal values across the entire surface. This object is achieved by the use of a transfer layer according to the characterizing part of claim 1.